1. Field of the Invention
The present invention relates to a pointing device for controlling the movement of a cursor displayed on a display device.
2. Description of the Related Art
Pointing devices are used in an appliance such as a personal computer, a work station, etc., for controlling the movement of a cursor displayed on a display device in response to an operator changing the position of a stick provided on an outer surface of the appliance. Such a pointing device is used in a force detecting device as disclosed, for example, in Japanese patent laid open No. Hei-4-148833. This force detection device is provided with a sensor for detecting respective changes in an operating load in an X direction and a Y direction resulting from an operator's action, a converter for converting the detected change amounts into voltages, and an amplifier section for amplifying the converted voltages.
However, in this prior art pointing device, the cursor speed is determined in response to the size of a load applied to the sensor by an operator, using a reference voltage calculated using a fixed coefficient. Accordingly, when the coefficient is initialized with emphasis on the case when the operating load is large, the cursor speed is too fast, and it is difficult to stop the cursor at a desired position on the screen. Conversely, when the coefficient is initialized with emphasis on the case when the operating load is small, it takes a long time to move the cursor to a position which is far away.
Also, with this prior art pointing device, an offset voltage which becomes a value for detecting the change in the operating load voltage is initialized immediately after start-up of the control device. However, it is assumed that the load applied to the sensor is zero immediately after start-up of the control device, but in actual fact there is a situation where a slight load is being applied to the sensor. For example, if some sort of load due to the operator's unconscious touch on the stick, etc., is being applied to the sensor when the offset voltage is initialized, an inappropriate offset voltage is initialized. If the offset voltage is initialized to an inappropriate value in this way, a situation arises where the cursor does not move if a very weak load is applied to the sensor when the operator intends to move the cursor at a slow speed.
Another problem with this prior art pointing device is that an offset voltage that is initialized immediately after start-up of the above mentioned control device gradually changes during operation of the appliance, due to changes in circuit characteristics caused by environmental temperature variations. If the offset voltage changes in this way, the ratio of operating load to cursor speed is not uniform in the X direction and Y direction, and a situation arises where the cursor moves even when the sensor is in a non-operating state.